The XB-60 was ordered by the Air Force as a precaution against some unforeseen catastrophic failure in the B-52. With a 72 percent commonality with the veteran B-36, a swept wing and tail were substituted, and eight J57 jet engines were added, resulting in a 508-mph bomber that was totally outclassed by the B-52. Convair bounced back, however, and proceeded with the beautiful supersonic B-58 Hustler.

출처는 같습니다 ^^